In one aspect of the invention, a bearing retention assembly is provided. The postal articles inside the pile compartment rest against said pile compartment wall. The first through third components are all situated within the surface layer, which is provided as a single surface layer, such that all of the components are in close proximity to one another within the single surface layer. The light-transmissive sheet-like body itself or an edge thereof can be detected with high accuracy even if the light-transmissive sheet-like body has a high transmittance.